1. Field of the Invention
The present invention relates to a sheet feeder for attachment to a printer which is placed on top of the sheet feeder and more particularly to a sheet feeder which includes multiple bins or cassettes in which stacks of sheets are disposed and a pair of which contain movable trays which are slantly disposed and resiliently coupled to the frame of the sheet feeder in order to hold and selectively feed a variety of sizes of sheets to the printer.
2.Description of the Prior Art
Sheet feeders are used to handle a wide variety of materials such as cut sheets, preprinted forms, envelopes, and continuous computer sheets. As office systems are now more and more automated and computerized, an increasing number of sheet feeders have been recently made available. A majority of the sheet feeders has so far been used for copying machines. A comparatively smaller number of sheet feeders for printer application has been made available. Printers are sometimes called electronic typewriters and are producing a growing percentage of office written output. The sheet feeders for these printers should be efficient and convenient to use.
The sheet feeder which U.S. Pat. No. 4,248,415 teaches is typical of most of the presently available cut sheet feeders which are placed on top of the printers and electronic typewriters. These printer-top sheet feeders hold a comparatively small capacity of sheets and have coherent problems of sheet separation. In other words, with printer-top sheet feeders one or more sheets tend to be carried along by inter-sheet frictional forces with the one sheet which alone should be fed because the feed direction is generally downward thereby the force of gravity tends to help extra sheets to be dragged down. Printer-top sheet feeders have a disadvantage of blocking the printed sheet paths leading to sheet stackers which may be disposed behind the printers. Therefore, a printer-top sheet feeder normally has a small capacity printed sheet collector in the front section of the sheet feeder. Most office printers accept both cut sheets and continuous sheets. However, automatic cut sheet feeders for printers do not normally possess a provision for holding and feeding a continuous sheet. A conventional cut sheet feeder must often be removed when a continuous sheet is fed in place of cut sheets.
U.S. Pat. No. 4,248,415, entitled Apparatus for Feeding Sheets of Paper from a Magazine to a Printing Office Machine, issued to Helmut Steinhilber on Feb. 3, 1981, teaches an apparatus for feeding single sheets of paper to a printing office machine, for example a typewritter or a bookkeeping machine. The paper is held in a stack within one or more magazine and the top sheet of the stack is engaged by a separating roller which is driven by a gear belt from the printing platen or another rotating part of the associated office machine. In order to insure the exact positioning at the entrance of the printing platen slot of the sheets of paper delivered by the separating roller, the apparatus provides that when the separating roller transports a sheet of paper forward to the printing platen the printing platen is rotating backward at that time thereby preventing entry of the new sheet while insuring the position as the continued motion of the separating roller causes the new sheet to bulge. Thereafter, the direction of rotation of the printing platen is reversed causing the reliable advance of the paper into the printing office machine. During this time, an overrunning clutch prevents reverse motion of the separating roller. In order to provide for limited reversal of motion of the printing platen during the printing process, a lost motion mechanism in the drive of the separating roller permits limited paper reversal.
U.S. Pat. No. 4,232,860, entitled Paper Feeder, issued to Frank H. Brown on Nov. 11, 1980, teaches a top-load, bottom-feed friction feeder which includes a power source having connected thereto a main feed wheel and an eccentric wheel. A stone wheel is located adjacent to the main feed wheel and can be adjusted so that the feeder can continuously feed pieces which have a wide variety of sizes, stocks and orientation.
U.S. Pat. No. 4,240,622, entitled Mechanism for Transporting Sheetlike Recording Carriers, issued to Albert Rutishauser on Dec. 23, 1980, teaches a sheet transporting magazine for automatic typewriters or the like with a three point bar structure for arching a stack of sheets in the conveyance direction while disposed in the magazine to prevent the sheets from canting laterally in the magazine.
U.S. Pat. No. 4,310,151, entitled Sheet Feeding Apparatus, issued to Sakae Fujimoto on Jan. 12, 1982, teaches a sheet feeding apparatus which includes a vertically movable vacuum plate which has opening for sucking sheets individually and which allows sheet feeding rollers to extend therethrough for translating the sucked sheet wherein a sheet pressing portion is formed in the vacuum plate to form a space between the forward end portions of the sheets and the vacuum plate prior to the suction of the sheets. In another embodiment, instead of the sheet pressing portion, a sheet feeding roller which is mounted on the vacuum plate is utilized as the sheet pressing element so that the sheets are pressed before being sucked causing the suction force to be applied to the forward end portions of the sheets.
U.S. Pat. No. 4,312,503, entitled Spring-Loaded Friction Retard Separator, issued to Allan L. Saxinger, Clayton M. Haight and Barry C. Kockler on Jan. 26, 1982, teaches a sheet feeding and separating apparatus for separating a single sheet from a stack of sheets and forwarding the separate sheet away for subsequent processing. The apparatus includes a feed belt which is disposed adjacent to the stack for contacting the top sheet in order to separate the top sheet from the stack. A retard shoe is resiliently biased into engagement with the feed belt. Actuation of the feed belt and engagement of the retard shoe with the sheets provide a rotating and locking relation with the mounting member of the retard shoe thereby preventing passage of multiple sheets by the feed belt but allowing the fed sheet to be pulled from the apparatus by a low amount of pulling force.
U.S. Pat. No. 4,211,398, entitled Feeders for Cardboard and Like Blanks, issued to Thomas D. Bishop on July 8, 1980, teaches a feed having two stack which are top feed by reciprocating suction boxes. The stacks feed alternately and a belt is used to transfer blanks from the rear stack.
U.S. Pat. No. 4,310,152, entitled Stacker for Film Material, issued to Wilhelm Mitzel on Jan. 12, 1982, teaches a stack for sheet material which has a stacker drum. The stacker drum receives sheet from a transport system at a first tangential position and arcuately moves them to a stop at a second tangential position against which the stack is formed. The stacker drum has a row of suction openings for gripping the leading edge of the sheets followed by compressed air openings which are positioned behind the suction openings sufficiently far so that the compressed air is applied to the sheets only after the leading edges have been run up against the stop.
U.S. Pat. No. 4,236,709, entitled Cartridge Sheet Feed Attachment, issued to Ronald E. Hunt on Dec. 2, 1980, teaches a compact sheet feeding apparatus which is suitable for attachment to a printer and which includes a removable cartridge for holding a stack of sheets. The cartridge provides an integral edge aligner surface and second sheet restraint during lateral shingling of sheets prior to feeding in a direction transverse to shingling.
U.S. Pat No. 4,245,831, entitled Adjustable Tray, issued to Stephen F. Michatek on Jan. 20, 1980, teaches a tray which receives and guides document sheets that are being manually fed to a copier/dupicator or printer. The tray has a plurality of flexible segments which are movable in pairs for adjusting the size of the guide surface so that sheets of several sizes can be accommodated by the tray.
U.S. Pat. No. 4,221,375, entitled Copy Sheet Handling Apparatus for a Copier, issued to Douglas I. Morrison and William Gergely, Jr. on Sept. 9, 1980, teaches a copy sheet handling apparatus which includes a pair of feed rollers spaced apart from each other, and a copy sheet tray which extends substantially transversely through a plane which, in turns, extends midway between the feed rollers. The copy sheet handling apparatus also includes a structure for swivelably supporting the tray in the aforesaid plane and mechanisms, which are coupled to the structure, for applying a resilient force to the tray substantially in the aforesaid plane in order to move the tray toward the feed rollers for disposition of a copy sheet into engagement with the feed rollers whereby the force is substantially equally distributed between the feed rollers.
Today's office printers are most often used for typing letters. There are kinds of letter sheets, normally one with a letter head for the first page and another for succeeding pages. Therefore an almost mandatory requirement for an efficient automatic sheet feeder for office printers is a capability of feeding cut sheets from either of two stacks of sheets selectively one at a time. It should be a preferrable feature that a sheet feeder accommodates a variety of sizes of sheets without its mechanism being too complicated.
In many instances printers are disposed on dedicated stands which have empty spaces within their frames. Such empty spaces should be ultilized if possible.
An advantage of a sheet feeder which is disposed under the printer wherein the sheets are fed through the bottom of the printer is that a printer-top sheet feeder may also be utilitized simultaneously in addition to the underprinter sheet feeder when an additional type of sheets, such as envelopes and cut sheets of additional kinds, are required.